we are tyco integrated security. and we are sharper. then you'll love lactose-free lactaid® it's 100% real milk that's easy to digest so you can fully enjoy the dairy you love. lactaid®. for 25 years, easy to digest. easy to love. >>> in the wake of the boston bombings, federal investigators are on the ground, combing through evidence to learn more about the explosive devices and ultimately who was behind this attack. for more on the investigation, joining me from washington, former director of the national terrorism center, michael leiter. he's also an nbc national security analyst. thank you for being here. >> good morning. >> as this investigation gets underway, what steps are investigators taking right now to try to piece this all together? >> the investigators are obviously going to start at the scene. they're going to secure that area as the mayor and police chief have said. that will be a wide cordon. they want to get as much evidence as they can from the devices themselves and the fragments they left. that's important for unde